public static void main(String[] args){
    SwingUtilities.invokeLater(new Runnable(){
        public void run(){
            LeftoverExample.createGUI();
        }
    });
}

public static void createGUI(){
    JFrame jF = new JFrame();
    jF.setSize(new Dimension(500,500));
    jF.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    //GBL Example
    JPanel gBLExamplePanel = new JPanel();
    GridBagLayout gBL = new GridBagLayout();
    gBL.columnWidths = new int[]{0};
    gBL.rowHeights = new int[]{50};
    gBLExamplePanel.setLayout(gBL);

    //Initial Constraints
    GridBagConstraints gBC = new GridBagConstraints();
    gBC.fill = GridBagConstraints.BOTH;
    gBC.gridx = 0;
    gBC.gridy = 0;
    gBC.weightx = 1;
    gBC.weighty = 0;
    gBC.insets = new Insets(0, 0, 0, 0);

    //Add to GBL Panel
    LeftoverExample.addButtons(gBLExamplePanel, gBC);
    LeftoverExample.addButtons(gBLExamplePanel, gBC);
    LeftoverExample.addButtons(gBLExamplePanel, gBC);

    //BoxLayout Example
    JPanel boxLayoutExamplePanel = new JPanel();
    boxLayoutExamplePanel.setLayout(new BoxLayout(boxLayoutExamplePanel, BoxLayout.X_AXIS));

    //Add to BoxLayout Panel
    LeftoverExample.addButtons(boxLayoutExamplePanel);
    LeftoverExample.addButtons(boxLayoutExamplePanel);
    LeftoverExample.addButtons(boxLayoutExamplePanel);

    //Add Panels to ContentPane
    jF.getContentPane().add(gBLExamplePanel);
    jF.getContentPane().add(boxLayoutExamplePanel, BorderLayout.SOUTH);

    //Final
    jF.setVisible(true);
}

private static JButton createButton(Color c){
    JButton jB = new JButton();
    jB.setBackground(c);
    jB.setMaximumSize(new Dimension(Integer.MAX_VALUE, Integer.MAX_VALUE));
    return jB;
}

private static void addButtons(JComponent jC, GridBagConstraints gBC){
    //Create Buttons
    Color[] colorA = {Color.RED, Color.BLUE, Color.BLACK, Color.GREEN};
    for(Color c : colorA){
        jC.add(LeftoverExample.createButton(c), gBC);
        gBC.gridx++;
    }
}

private static void addButtons(JComponent jC){
    //Create Buttons
    Color[] colorA = {Color.BLUE, Color.BLACK, Color.GREEN, Color.RED};
    for(Color c : colorA){
        jC.add(LeftoverExample.createButton(c));
    }
}